1. Field of the Invention
The present invention relates to a system for evoking a desired electroencephalogram signal, e.g., an alpha rhythm, from the brain of a human being to bring the human being into a relaxed condition.
2. Prior Art
It is known in the art that brain waves, i.e., electroencephalogram (EEG) signals, originating in the brain of a human being and the physiological and psychological states of the human being are closely related to each other. For example, when a human being is awake and in an active mental state, beta (.beta.) rhythms in a frequency range of from about 13 to 30 Hz are dominantly produced. Alpha (.alpha.) rhythms are prevalent in a relaxed mental state and have a frequency ranging from about 8 to 13 Hz. Brain waves generated during drowsiness and lightsleep are theta (.theta.) rhythms in a frequency band ranging from about 4 to 7 Hz. The correlation between these brain waves having different frequency ranges and certain human activity phases indicates that the evocation of a certain brain wave through sensory stimulation is apt to put the human being in a corresponding physiological and psychological state.
Based on the analysis of the interaction between the EEG signals and physiological and psychological states, there have heretofore been proposed various systems for evoking alpha waves from the brain of a human being by giving a certain external stimulus to his body, thereby to place him in a physically and psychologically relaxed state for assisting him in lessening stresses and achieving mental concentration.
For example, U.S. Pat. No. 4,315,502 discloses an EEG signal evoking system comprising a pair of goggles having lamps disposed around the lenses, a pair of headphones, and a pulse signal generating means for outputting a predetermined pulse signal to the goggles and headphones. In use, the goggles and headphones are worn by a user, and a pulse signal is applied to the goggles and headphones by the pulse generator. When the lamps on the goggles and the headphones are energized with the pulse signal, external stimulus in the form of flickering light and sound are applied to the user, thus evoking a desired brain wave to bring the user into a relaxed mental state.
With the above conventional EEG signal evoking system, the EEG evoking stimulus signal is artificially generated according to a predetermined pattern irrespective of the nature of the brain waves of the user, and such artificial stimulating pulses are applied to the user for the evocation of the desired EEG rhythm. Therefore, the evoking effect of the known EEG evoking system differs from user to user, and the evoking efficiency of the system is not the same among various users.